It can be highly desirable in the context of electronic warfare (“EW”), as well as under various other circumstances, to monitor a broad electromagnetic spectrum of interest so as to detect the presence, behavior, and properties of electromagnetic (“EM”) signals transmitted by EM sources that are within detection range of an EM signal receiver and in some examples are not known a priori to a user. Such EM signal receivers are generally tunable over the entire spectrum of interest, but use a reception bandwidth that is significantly narrower than the spectrum of interest, such that they must be frequently retuned between various frequencies within the spectrum so as to sample the EM activity throughout the entire spectrum of interest. This process of frequent retuning of a receiver within a broad spectrum of interest is referred to herein as “scanning,” and the timing and frequency pattern of the scanning is referred to herein as the “scan schedule.”
Often, the spectrum of interest is divided into a plurality of contiguous frequency “channels,” each of which is narrower than the bandwidth of the signal receiver, and the signal receiver is shifted between the center frequencies of these channels according to the scan schedule.
Various goals can motivate the monitoring of a spectrum of interest by an EM receiver. These can include determining the number of EM sources that are within detection range, determining the locations of the EM sources, determining the apparent types of the EM sources (as indicated by characteristics of their transmitted signals), or any combination thereof. Under EW conditions, for example, scanning can be helpful for determining numbers and types of nearby hostile assets, intercepting adversary communications for intelligence analysis, directing jamming signals that interfere with adversary communications, and/or avoiding hostile jamming efforts.
Often, transmissions from some EM sources may be of little or no interest, while transmissions from other EM sources may be of high interest. Accordingly, relative degrees of interest may be assigned to various EM sources, whereby detection of EM signals of highest interest are given priority, while signals from other EM sources are given secondary importance or ignored completely.
Typically, a system that is used to scan and monitor a spectrum of interest includes an EM signal receiver that detects and records EM transmissions, a controller that controls the EM signal receiver and implements the scan schedule, and possibly also a companion system that analyzes the received signals so as to extract information therefrom, which may include distinguishing types of EM sources and determining their relative degrees of interest.
If all of the EM sources of interest that are within detection range of an EM signal receiver are relatively persistent in time and constant in broadcast frequency, then it can be a simple matter to scan through the spectrum of interest, identify the signals of interest, and implement a scan schedule that is mainly limited to the frequencies where the signals of interest have been detected, while possibly repeating a full scan of the spectrum of interest at intervals so as to detect the arrival of any new EM sources of interest.
However, it is increasingly common for EM signals of interest to be transient in time and/or variable in transmission frequency. For example, transmissions that originate from aircraft may move in and out of range relatively quickly. RADAR signals may vary in their transmitted direction, and therefore may be detected with an amplitude that is periodic or otherwise variable. Transmissions that originate from ground-based vehicles may also be intermittent in both amplitude and time as the vehicles change location, and as various intervening obstructions temporarily interrupt the transmitted signals. In addition, many transmissions of interest in an EW environment employ frequency “hopping” according to a pseudo-random pattern that renders detection, jamming, and signal interception more difficult.
Accordingly, efficient monitoring of signals of interest in an EW environment often depends upon accurate predictions of future transmission patterns based upon a sophisticated analysis of previously received signals.
One approach is to collect and analyze a quantity of EM signal detections, construct a scan schedule using some combination of computational and manual resources, and then configure a controller to cause a signal receiver to implement the scan schedule. This approach can be effective when the EM sources of interest are relatively consistent in their behavior over time.
However, as EM sources of interest have become increasingly more sophisticated, their behavior has become increasingly variable, causing the efficacy of such pre-determined scan schedules to degrade rapidly, and requiring frequent updates to the scan schedule based on newly acquired data. Often, the time required to develop new scan schedules, especially when human resources are applied, lags behind the rate at which EM sources vary their behavior, leading to degradation of scan performance.
What is needed, therefore, is a method of rapidly updating a scan schedule for an EM signal receiver that will optimize the receipt of signals of interest based on predictions of EM source behavior even when said behavior is variable.